This proposal is for a study to investigate the fetal electrocardiogram. We will study both the differences between different fetal electrocardiograms and changes in the fetal electrocardiogram during development of the fetus. Although there have been many studies of the fetal electrocardiogram to date, the primary emphasis has been on the fetal heart rate, especially during active labor; or the emphasis has been on the determination of viability or presentation. No data is available on the development of the wave form of the fetal ECG during the course of pregnancy. We will study the magnitude and the wave shape of the fetal electrocardiogram from as early as possible in pregnancy, and follow this pattern in the same patients through to just prior to delivery. We will thus establish the normal wave form and magnitude of the fetal ECG and subsequently correlate abnormalities in size and shape with problems during pregnancy, labor or the perinatal period. Because of the difficulty of recording good patterns using abdominal electrodes during labor our study primarily will be limited to the period up to active labor. Follow-up studies, sufficient to evaluate the status of the newborn, will be conducted. It is expected that eventually congenital abnormalities and/or fetal distress may be detected early in pregnancy using the fetal electrocardiogram.